mm/damon: Trivial fixups and improvements

When wrong scheme action is requested via the debugfs interface, DAMON prints an error message. Because the function returns error code, this is not really needed. Because the code path is triggered by the user specified input, this can result in kernel log mistakenly being messy.

To avoid the case, this commit removes the message

Fixes af122dd8f3c0 ("mm/damon/dbgfs: support DAMON-based Operation Schemes")

Signed-off-by SeongJae Park <[email protected]>

---
  mm/damon/dbgfs.c | 4 +---
  1 file changed, 1 insertion(+), 3 deletions(-)

mm/damon/dbgfs.c +1 -3

index 4bf4204444ab..5b628990ae6e 100644
@@ -210,10 +210,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
  				&wmarks.low, &parsed);
  		if (ret != 18)
  			break;
-		if (!damos_action_valid(action)) {
-			pr_err("wrong action %d\n", action);
+		if (!damos_action_valid(action))
  			goto fail;
-		}
 
  		if (min_sz > max_sz || min_nr_a > max_nr_a || min_age > max_age)
  			goto fail;

Hi park:

Quoted 4 lines · SeongJae Park

When wrong scheme action is requested via the debugfs interface, DAMON prints an error message. Because the function returns error code, this is not really needed. Because the code path is triggered by the user specified input, this can result in kernel log mistakenly being messy.

Completely correct, but there will also be a problem that users can’t quickly locate where the problem is,

Especially too many parameters need to be written into the interface.

I think it is necessary to add some debugging methods to help users find the error without polluting the kernel log.

And i have an idea, like this:

in dbgfs, add a last_cmd_stat interface.

     # echo "1 2 1 2 1 2  1 2 1 2 100 ..."  > schemes

# cat last_cmd_stat

# wrong action 100

In this way, on the one hand, it will not pollute the kernel log, on the other hand, it will help users find the cause of the operation interface error.

Park, how do you think of about this idea, if ok, i will send a patch.

Quoted 25 lines

To avoid the case, this commit removes the message

Fixes af122dd8f3c0 ("mm/damon/dbgfs: support DAMON-based Operation Schemes")

Signed-off-by SeongJae Park <[email protected]>

---
  mm/damon/dbgfs.c | 4 +---
  1 file changed, 1 insertion(+), 3 deletions(-)

mm/damon/dbgfs.c +1 -3

index 4bf4204444ab..5b628990ae6e 100644
@@ -210,10 +210,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
  				&wmarks.low, &parsed);
  		if (ret != 18)
  			break;
-		if (!damos_action_valid(action)) {
-			pr_err("wrong action %d\n", action);
+		if (!damos_action_valid(action))
  			goto fail;
-		}
 
  		if (min_sz > max_sz || min_nr_a > max_nr_a || min_age > max_age)
  			goto fail;

Signature · 2 lines

Best Regards!
Xin Hao

On Wed, 8 Dec 2021 14:29:40 +0800 Xin Hao <[email protected]> wrote:

Hi Xin,

Quoted 25 lines

Hi park:

Quoted 4 lines · SeongJae Park

When wrong scheme action is requested via the debugfs interface, DAMON prints an error message. Because the function returns error code, this is not really needed. Because the code path is triggered by the user specified input, this can result in kernel log mistakenly being messy.

Completely correct, but there will also be a problem that users can’t quickly locate where the problem is,

Especially too many parameters need to be written into the interface.

I think it is necessary to add some debugging methods to help users find the error without polluting the kernel log.

And i have an idea, like this:

in dbgfs, add a last_cmd_stat interface.

      # echo "1 2 1 2 1 2  1 2 1 2 100 ..."  > schemes

# cat last_cmd_stat

# wrong action 100

Quoted 5 lines

In this way, on the one hand, it will not pollute the kernel log, on the other hand, it will help users find the cause of the operation interface error.

Park, how do you think of about this idea, if ok, i will send a patch.

Thank you always for your great suggestions and efforts! BTW, I prefer to be called with my first name ;)

I want DAMON kernel code to be as simple and small as possible, while putting fancy but complicated features for user conveniences in user space tools like DAMO[1]. In other words, I hope the DAMON debugfs interface to be used as an interface for such user space tools, not an interface for human hands.

IMHO, implementing the feature you proposed in the kernel could make the code slightly bigger, while it can easily implemented in user space. I therefore think the feature would be better to be implemented in user space. If you could send a pull request of the feature for DAMO, it would be so great.

[1] https://github.com/awslabs/damo

Thanks,
SJ

Quoted 28 lines

Quoted 24 lines

To avoid the case, this commit removes the message

Fixes af122dd8f3c0 ("mm/damon/dbgfs: support DAMON-based Operation Schemes")

Signed-off-by SeongJae Park <[email protected]>

---
   mm/damon/dbgfs.c | 4 +---
   1 file changed, 1 insertion(+), 3 deletions(-)

mm/damon/dbgfs.c +1 -3

index 4bf4204444ab..5b628990ae6e 100644
@@ -210,10 +210,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
   				&wmarks.low, &parsed);
   		if (ret != 18)
   			break;
-		if (!damos_action_valid(action)) {
-			pr_err("wrong action %d\n", action);
+		if (!damos_action_valid(action))
   			goto fail;
-		}
 
   		if (min_sz > max_sz || min_nr_a > max_nr_a || min_age > max_age)
   			goto fail;

Signature · 2 lines

Best Regards!
Xin Hao

Hi SeongJae:

Quoted 29 lines · SeongJae Park

On Wed, 8 Dec 2021 14:29:40 +0800 Xin Hao <[email protected]> wrote:

Hi Xin,

Quoted 25 lines

Hi park:

Quoted 4 lines · SeongJae Park

When wrong scheme action is requested via the debugfs interface, DAMON prints an error message. Because the function returns error code, this is not really needed. Because the code path is triggered by the user specified input, this can result in kernel log mistakenly being messy.

Completely correct, but there will also be a problem that users can’t quickly locate where the problem is,

Especially too many parameters need to be written into the interface.

I think it is necessary to add some debugging methods to help users find the error without polluting the kernel log.

And i have an idea, like this:

in dbgfs, add a last_cmd_stat interface.

      # echo "1 2 1 2 1 2  1 2 1 2 100 ..."  > schemes

# cat last_cmd_stat

# wrong action 100

Quoted 7 lines

Quoted 5 lines

In this way, on the one hand, it will not pollute the kernel log, on the other hand, it will help users find the cause of the operation interface error.

Park, how do you think of about this idea, if ok, i will send a patch.

Thank you always for your great suggestions and efforts! BTW, I prefer to be called with my first name ;)

Ha-Ha, Sorry!

Quoted 5 lines

I want DAMON kernel code to be as simple and small as possible, while putting fancy but complicated features for user conveniences in user space tools like DAMO[1]. In other words, I hope the DAMON debugfs interface to be used as an interface for such user space tools, not an interface for human hands.

Ok, I know what you mean.

Quoted 1 line

Quoted 4 lines

IMHO, implementing the feature you proposed in the kernel could make the code slightly bigger, while it can easily implemented in user space. I therefore think the feature would be better to be implemented in user space. If you could send a pull request of the feature for DAMO, it would be so great.

Ok, i will do it, But there's a problem here, If the user does not use the DAMO tools to operate the dbgfs interface,

the operation interface error will still hard to find the cause of errors.

Quoted 35 lines

[1] https://github.com/awslabs/damo

Thanks,
SJ

Quoted 28 lines

Quoted 24 lines

To avoid the case, this commit removes the message

Fixes af122dd8f3c0 ("mm/damon/dbgfs: support DAMON-based Operation Schemes")

Signed-off-by SeongJae Park <[email protected]>

---
   mm/damon/dbgfs.c | 4 +---
   1 file changed, 1 insertion(+), 3 deletions(-)

mm/damon/dbgfs.c +1 -3

index 4bf4204444ab..5b628990ae6e 100644
@@ -210,10 +210,8 @@ static struct damos **str_to_schemes(const char *str, ssize_t len,
   				&wmarks.low, &parsed);
   		if (ret != 18)
   			break;
-		if (!damos_action_valid(action)) {
-			pr_err("wrong action %d\n", action);
+		if (!damos_action_valid(action))
   			goto fail;
-		}
 
   		if (min_sz > max_sz || min_nr_a > max_nr_a || min_age > max_age)
   			goto fail;

Signature · 2 lines

Best Regards!
Xin Hao

Signature · 2 lines

Best Regards!
Xin Hao

The DAMON virtual address space monitoring primitive prints a warning message for wrong DAMOS action. However, it is not essential as the code returns appropriate failure in the case. This commit removes the message to make the log clean.

Fixes 6dea8add4d28 ("mm/damon/vaddr: support DAMON-based Operation Schemes")

Quoted 7 lines · SeongJae Park

The DAMON virtual address space monitoring primitive prints a warning message for wrong DAMOS action. However, it is not essential as the code returns appropriate failure in the case. This commit removes the message to make the log clean.

Fixes 6dea8add4d28 ("mm/damon/vaddr: support DAMON-based Operation Schemes")

I don't think there should be a Fixes tag since it's not a serious bug.

Quoted 7 lines · On Fri, 3 Dec 2021 11:01:36 +0800 Muchun Song <[email protected]> wrote:

Quoted 6 lines · SeongJae Park

The DAMON virtual address space monitoring primitive prints a warning message for wrong DAMOS action. However, it is not essential as the code returns appropriate failure in the case. This commit removes the message to make the log clean.

Quoted 3 lines

Quoted 1 line

Fixes 6dea8add4d28 ("mm/damon/vaddr: support DAMON-based Operation Schemes")

I don't think there should be a Fixes tag since it's not a serious bug.

"Fixes:" doesn't mean "backport to stable". At least, not for MM patches. Other subsystems do get their Fixes:-tagged patches automatically backported.